1. Field of the Invention
This invention relates to crop harvesting machines and is more particularly concerned with such machines which are fitted with apparatus for detecting the passage of foreign objects. More especially, the present invention is concerned with the provision of means for automatically stopping the drive to certain components of such a crop harvesting machine upon the detection of a foreign object.
2. Description of the Prior Art
A variety of objects such as stones, pieces of wood, plastics and metal may lie in the path of harvesting machines which cut or pick-up a crop and these are liable to cause damage to the crop processing means within the machines. Harvesting machines which are particularly subject to such damages are forage harvesters. The crop processing means in a forage harvester comprise a cutterhead and an associated shearbar. These crop processing means are of a precision character, have fine clearances, and are buried in the body of the machine, whereby access thereto is somewhat difficult. Such processing means normally also operate at a high speed and have a great inertia so that severe damage can be caused by metallic foreign objects before the components in question can be arrested. Pieces of wood are not generally a serious hazard. Stones are more so but generally splinter though causing chipped blades on the cutterhead. Plastics and non-ferrous metals are rare, and in any event relatively soft and hence not hazardous. Thus the main risk arises from ferrous metal objects which are both numerous and harmful. Such undesirable objects may be whole or broken components that have become detached from machines, tools left lying in a field or that have bounced out of moving machines, hitch pins, fencing stakes and scrap dumped by intruders. The high present-day level of mechanisation and the pressures on a diminishing labour force, have lead to an increased risk of ferrous scrap in all areas, augmented near towns by habits of disposal.
Whether or not they cause damage to a machine, metal objects passing through will find their way into the processed crop and may, therefore, ultimately injure livestock fed with it so that from all standpoints such objects need to be excluded.
Metal detectors in general, and metal detectors applied to forage harvesters, are already known in the art. However, in general, prior art devices for detecting the presence of metallic, ferrous, or other objects have one or more inherent disadvantages rendering them of little value in certain applications, especially in the reliable protection of expensive crop harvesting machinery from tramp metal. Such prior art devices often operate with high excitation frequencies and are susceptible to the presence of moisture, various types of vegetation, vibration, or the like. They, therefore, impose on the operator of a machine the serious burden of continuous monitoring and adjustment of the calibration of the detector. Even at relative low excitation frequencies such detectors are adversely affected to a significant extent by an over-extensive scanning area, thereby rendering them unusable for use where high accuracy, reliability and freedom from generation of false alarms is demanded. Additionally, prior art detection devices are located at positions which, for one reason or another, may fail adequately to detect the presence of incoming foreign objects. An example of a detection device located at a position within a crop harvesting machine which has been found less than satisfactory is illustrated in U.S. Pat. No. 3,757,501. This patent teaches the use of a detection device mounted in the floor plate of the header used with the harvester. This location permits undesirable objects which may be located on top of the incoming mat of crop material to go undetected. Further, this location creates the situation where each attachment, i.e. the header, would have to incorporate the detection device rather than it being standard equipment in the body of the forage harvester, thereby increasing the cost to the farmer.
It is also known to use blocking means in combination with metal detectors on forage harvesters, whereby on detection of an undesirable object the drive means for the feeder mechanism is immediately blocked. In this event a safety clutch in the drive line is rendered operative. Thus the movement of the crop feeder mechanism is stopped abruptly and hence also the layer of crop material with the undesirable object therein, which was progressing to the cutterhead, is stopped instantaneously. This of course prevents the undesirable object causing damage to the cutterhead and/or being mixed with the silage. This also enables the operator to reverse the feeder drive mechanism to remove the undesirable object. However, this abrupt blocking of the drive line of the feeder mechanism may be harmful to the drive means itself. Also, as long as the operator does not take appropriate action, the safety clutch continues slipping and prolonged slipping is, of course, undesirable. Furthermore, after the drive to the feeder mechanism has been stopped as a result of operation of the detection device it could be that, rather than reversing the drive to the feeder mechanism to remove the undesirable object, the operator re-engages the feeder drive in the normal working direction by mistake. This, of course, results in the undesirable object being fed to the cutterhead where it may cause damage, or, if it does not cause damage, it is chopped into small pieces and mixed with the silage.
In other known arrangements, the metal detector on a forage harvester has been combined with a feeder drive blocking device and an electric actuator which operates as soon as an undesirable object is detected. The electric actuator is coupled to a slip clutch mechanism in the drive line of the feeder mechanism and is operative upon detection of an undesirable object progressively to disengage the clutch mechanism. As long as the clutch mechanism is not entirely disengaged, it is slipping. Again, as was the case in the other above described prior art structure, the drive line and the clutch mechanism are subjected to heavy peak loads. Also, the safety clutch mechanism may continue to slip for a relatively long period of time and the operator may make a mistake by re-engaging the drive for the feeder mechanism in the normal operative direction without first having reversed that drive.
A prior art metal detection device used on a forage harvester is described in detail in British Patent Specification No. 2,013,072 A. The present invention aims at improving and simplifying this device and the associated drive stopping mechanism.